Food Irradiation

Food Irradiation

Food irradiation is a technology for controlling spoilage and eliminating food-borne pathogens, such as salmonella. The result is similar to conventional pasteurization and is often called "cold pasteurization" or "irradiation pasteurization." Like pasteurization, irradiation kills bacteria and other pathogens, that could otherwise result in spoilage or food poisoning. The fundamental difference between the two methods is the source of the energy they rely on to destroy the microbes. While conventional pasteurization relies on heat, irradiation relies on the energy of ionizing radiation. The FDA emphasizes that no preservation method is a substitute for safe food handling procedures.

How is food irradiated?

Bulk or packaged food passes through a radiation chamber on a conveyor belt. The food does not come into contact with radioactive materials, but instead passes through a radiation beam, like a large flashlight.

The type of food and the specific purpose of the irradiation determine the amount of radiation, or dose, necessary to process a particular product. The speed of the belt helps control the radiation dose delivered to the food by controlling the exposure time. The actual dose is measured by dosimeters within the food containers.

Cobalt-60 is the most commonly used radionuclide for food irradiation. However, there are also large cesium-137 irradiators and the Army has also used spent fuel rods for irradiation.

What are the sources of radiation used?

Cobalt 60 Gamma Sources

Cobalt-60 emits ionizing radiation in the form of intense gamma rays. Gamma facilities" store it in stainless steel capsules (like "pencils" of cobalt), in underwater tanks. Cobalt-60 has several advantages:

up to 95% of its emitted energy is available for use

penetrates deeply

yields substantial uniformity of the dose in the food product

decays to non-radioactive nickel

considered to pose low risk to the environment.

However, its 5.3-year half-life offers disadvantages:

cobalt-60 "pencils" require frequent replenishment

treatment of the food is relatively slow.

Cesium-137 is a gamma source that is also used for irradiation. Cesium-137 has a less penetrating gamma beam and a longer half-life, making it more suitable under certain circumstances.

Electron Beam Generators

Electron beam facilities generate e-beams with an electron beam linear accelerator. (It works on the same principle as a television tube.) The electrons are concentrated and accelerated to 99% of the speed of light and energies of up to 10 MeV.

Because e-beams are generated electrically, they offer certain advantages:

they can be turned on only as needed

they do not require replenishment of the source as does cobalt-60

there is no radioactive waste

E-beam technology also has disadvantages:

shallow depth of penetration

e-beams must be converted to x-rays to penetrate large items such as carcasses

X-Ray Accelerators

X-ray facilities use an electron beam accelerator to target electrons on a metal plate. Although some energy is absorbed, the rest is converted to X-rays. Like gamma rays, X-rays are penetrating, and can be used on food boxes 15 inches thick or more. This allows food to be processed in a shipping container.

X-rays offer the advantage of high penetration, but share the other e-beam technology disadvantages.

Gamma and X-Rays
A a description of the properties, uses and health effects of gamma and x-rays

What is the radiation dose to the food?

Radiation doses vary for different foodstuffs. For the vast majority of foods, the limit is less than 10 kilo Gray. The U.S. Food and Drug Administration (FDA) sets radiation dose limits for specific food types:

Food Type

Dose (kilo Grays)

fruit

1

poultry

3

spices, seasonings

30

The dose limit for spices and seasons is higher, because they are consumed in very small quantities.

How does irradiation kill bacteria?

When ionizing radiation strikes bacteria and other microbes, its high energy breaks chemical bonds in molecules that are vital for cell growth and integrity. As a result, the microbes die, or can no longer multiply causing illness or spoilage.